ased on our results in the LCMV model of viral infection as well as in human HCV Infection it seems likely that viral escape mutations and a combination of molecules associated with T-cell dysfunction and inhibition are key contributors to viral persistence. Importantly, data in acute HCV infection indicate that HCV infection elicits both CD4 and CD8 T cell responses detectable in PBMC during early disease, but the responses decline quickly in persons who progress to chronic infection. In the liver, responses remain detectable, often for decades and at substantial frequencies, yet virus persists at high levels. Our overall hypothesis is that T-cell dysfunction is a major factor in failure to control HCV infection and that by combining both mouse and human studies of T cell dysfunction we can define key pathways or immunological defects underlying poor immunological control of HCV infection. To test this hypothesis we propose to further define the different subsets of T-cells associated with different levels of viral control with experiments in humans and mice informing each other. We will define the functional profile and expressions of a combination of inhibitory molecules using HCV-specific T-cells in human PBMC and liver derived T-cells based on recent findings in LCMV. In parallel we will further refine our murine model by differentiating in detail the transcriptional profiles of T-cells in different stages of dysfunction and different T-cell subsets. We will also establish transcription profiles of human T-cells and the datasets together will direct the future direction of our investigations. In addition to defining the properties of HCV-specific T-cells we will define how the liver environment in chronic HCV infection contributes to T-cell dysfunction and thus viral persistence, e.g. by the expression of T-cell inhibitory ligands or regulatory cytokines. In addition we will also investigate HCV-specific CD4+ T-cells that are equally critical for viral control but have been investigated in much less detail. These studies will be critical for understanding HCV pathogenesis, for guiding the design of prophylactic vaccines and immunotherapeutic interventions, but also for improved general model of persistent viral infections in humans.